Manufacture of Hydrofluoroalkanesulfonic Acids

ABSTRACT

A process for manufacture of hydrofluoroalkanesulfonic acid with at least one hydrogen bonded to the carbon atom adjacent to the carbon atom bonded to the sulfonic acid group comprising: contacting a fluoroolefin with sulfite in an aqueous solution adjusted to about pH 4 to pH 12; removing water from the solution to form a solid; directly treating the solid with oleum; and distilling the hydrofluoroalkanesulfonic acid therefrom. Also a process for manufacture of potassium hydrofluoroalkanesulfonate in high purity is described.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is in the field of strong acids useful for catalysis.

2. Description of Related Art

Trifluoromethanesulfonic acid is used for catalysis where a strong acidis needed. It offers a safer, more easily handled alternative to theinorganic acids, hydrogen fluoride and sulfuric acid, which are widelyused in industrial processes. Known hydrofluoroalkanesulfonic acids,such as tetrafluoroethanesulfonic acid (TFESA), could be more effectivecandidates to replace trifluoromethanesulfonic acid in catalyticapplications.

Hydrofluoroalkanesulfonic acids are made by the addition of the elementsof sulfurous acid, H₂SO₃, to fluoroolefins. For example, TFESA is theproduct of the reaction with tetrafluoroethylene (TFE):

CF₂=CF₂+H₂SO₃->HCF₂—CF₂SO₃H  (1)

In practice, the fluoroolefin is reacted with aqueous sulfite solution,usually an alkali metal sulfite. The solution is buffered to suppressthe competing reaction, hydration of the fluoroolefin to form acarboxylic acid byproduct. In the case of TFE, the acid resulting fromhydration is difluoroacetic acid, HCF₂CO₂H.

The literature does not provide an efficient manufacturing method forthis reaction. An early reference, U.S. Pat. No. 2,403,207 (1946),teaches the optional use of free radical initiator. A. Kilian and H.Waeschke in Wissenschaftliche Beiträge, Ingenieurhochschule Köthen, pp.22-28 (1978), teach the utility of peroxide initiator for the reaction.Borax is generally used as the buffer. Extraction, usually with ethanol,is used to recover the product salt or acid. Typically, the reactionmixture is worked up by drying, followed by extraction with hot ethanol.The extract is dried to remove the ethanol and the resulting solid istreated with sulfuric acid. This mixture is distilled to yield thehydrofluoroalkanesulfonic acid, usually as a hydrate if any water ispresent, and byproduct organic acid or acetate. If the unhydratedhydrofluoroalkanesulfonic acid is needed, a further step, such astreatment with thionyl chloride, is necessary. As late as 1995, ChinesePatent Application 1097191 noted the shortcomings of the availablemanufacturing methods (“harsh reaction conditions, low yield, lowreaction uniformity and high cost”) and proposed replacement of waterwith aqueous organic solutions and the use of organic ammonium compoundsin the reaction. These proposed modifications make the reaction morecomplex and expensive. Two years later and fifty years after the '207patent, Japanese Patent Application 9-104686 (1997) disclosedpreparative examples of the reactions with TFE and withhexafluoropropylene (HFP) with aqueous sulfite. Reaction times were 110hours and yields 20% or less.

A simplified process is needed for making hydrofluoroalkanesulfonicacids in good purity and yield.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a process for manufacture ofhydrofluoroalkanesulfonic acid with at least one hydrogen bonded to thecarbon atom adjacent to the carbon atom bonded to the sulfonic acidgroup comprising, a) contacting a fluoroolefin with sulfite in anaqueous solution adjusted to about pH 4 to pH 12; b) removing water fromthe solution to form a solid; c) directly treating the solid with oleumto form a mixture that includes hydrofluoroalkanesulfonic acid; and d)distilling the hydrofluoroalkanesulfonic acid from the mixture. Theprocess simplifies the recovery of the final product since extractivesteps and the attendant solvents can be eliminated.

Preferred processes according to this invention eliminate the use ofinitiators as being deleterious to the desired addition reaction, and/orbuffer the reaction without introducing extraneous reagents such asborax or phosphate, promoting rapid reaction with little or nobyproduct, and without contamination of the final product(hydrofluoroalkanesulfonic acid) by buffer-derived impurities.

The present invention further provides a process for manufacture ofpotassium hydrofluoroalkanesulfonate with at least one hydrogen bondedto a carbon atom adjacent to the carbon atom bonded to the sulfonategroup comprising: a) contacting fluoroolefin having at least threecarbon atoms with an aqueous solution of sulfite and counter ion inwhich the counter ion comprises potassium, said solution having a pH ofabout 4 to 12; and b) employing conditions which cause potassiumhydrofluoroalkanesulfonate to precipitate from said solution.

The present invention also provides potassium salts of R_(f)−CFH−CF₂SO₃⁻wherein R_(f) is selected from the group consisting of fluoroalkylgroups, perfluoroalkyl groups, cyclofluoroalkyl groups andcycloperfluoroalkyl groups, said groups optionally containing etheroxygen.

DETAILED DESCRIPTION OF THE INVENTION

Fluoroolefins employed according to this invention are olefins having atleast one fluorine atom bonded to a doubly-bonded carbon. Preferably,the fluoroolefin has a terminal double bond, i.e. has a vinyl group. Oneclass of fluoroolefins of this type has the formula: a) if acyclic,C_(n)F_(a)H_(b)X_(c) where X is a halogen, a≧1, b=0 to 2n−1, and c=0 to2n−1, and a+b+c=2n, at least one F being bonded to a doubly bondedcarbon atom, preferably being a vinyl F, that is a fluorine atom bondedto one of the carbon atoms of a vinyl group; b) if cyclic,C_(n)F_(a)H_(b)X_(c) where X is a halogen, a≧1, b=0 to 2n−3, and c=0 to2n−3, and a+b+c=2n−2, at least one F being bonded to a doubly bondedcarbon atom, preferably being a vinyl F. Examples of such fluoroolefinsare vinyl fluoride (VF), vinylidene fluoride (VF₂), trifluoroethylene,chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), andhexafluoropropylene (HFP).

A subset of the above class of fluoroolefins has the general formulaCF₂=CF−R. R may be hydrogen, alkyl with or without halogen substitutionsand, if so substituted, preferably with chlorine and/or fluorine,preferably fluoroalkyl, and more preferably perfluoroalkyl, and may belinear or branched, or cyclic.

Preferably the fluoroolefin has at least two vinyl fluorine atoms, andmore preferably, three. Preferably in the fluoroolefin at least about35% of the monovalent atoms are fluorine atoms, more preferably at leastabout 50%, more preferably still at least about 75%, and most preferablythe fluoroolefin is a perfluoroolefin. Preferably the fluoroolefin is analpha-fluoroolefin, that is an olefin in which the double bond is at theend of the olefin molecule. Preferred fluoroolefins are TFE and HFP.

TFE can be safely and conveniently shipped and stored as a mixture withcarbon dioxide (CO₂), as disclosed in U.S. Pat. No. 5,345,013. It is anadvantage of the process according to this invention that the mixture,sometimes called the shipping mixture, can be used without the need forisolating the TFE from CO₂.

The term sulfite (SO₃ ⁼) is used herein with the understanding that inaqueous solution this species is in equilibrium with bisulfite (HSO₃ ⁻).The ratio of sulfite to bisulfite is a function of the pH of thesolution. This equilibrium may also include sulfurous acid (H₂SO₃) andsulfur dioxide (SO₂). SO₃ ⁼/HSO₃ ⁻forms a buffer that with propercontrol can effectively buffer the reaction according to this inventionwithout the introduction of extraneous materials such as borax andphosphate, which can be the source of impurities in the product and, inaddition, add to the cost of ingredients, and increase the variety ofchemicals in the waste product, thus increasing the difficulty and costof disposal or recovery.

The optimum pH range for the formation of hydrofluoroalkanesulfonicacids according to this invention is about 4 to 12, preferably about 5to 11, more preferably about 5 to 10, and most preferably about 5 to 9.Optimum pH can be attained by adding a sulfite source such as sulfurdioxide (SO₂), sulfurous acid, bisulfite, and/or sulfite to water, andadjusting the pH by further addition of a reagent that does notintroduce extraneous materials into the reaction. By non-extraneousmaterial is meant a material that is related to the necessaryingredients of the reaction according to this invention, these beingwater, sulfite or sulfurous acid. Ingredients that are fugitive in thesense of being easily removed without contamination of the product orresidue, such as carbonate, bicarbonate, and/or carbon dioxide are notconsidered extraneous materials.

Such non-extraneous materials include hydroxide, carbon dioxide (CO₂),bicarbonate, carbonate, sulfuric acid, bisulfate, and sulfate, andsulfurous acid, bisulfite, and sulfite. If the initially made solutionhas too high a pH, one or more of the acidic types of materials listedabove, e.g. SO₂, sulfuric acid, bisulfate, or CO₂ are added. If theinitially made solution has too low a pH, one or more of the basic typesof materials listed above, e.g. hydroxide, sulfite, or carbonate, areadded.

CO₂ is a particularly effective reagent. When present, it acts to bufferthe reaction and suppress all but the desired product. It is believedthat it does this by reacting, in the form of carbonic acid (H₂CO₃) withwhich it exists in equilibrium in water, with hydroxyl (OH⁻) ion formedin the reaction of sulfite, the effective reactant, with fluoroolefin,e.g., TFE in equation (2) below:

CF₂=CF₂+SO₃ ⁼+H₂O->HCF₂—CF₂SO₃ ⁻+OH⁻  (2)

One mole of H₂CO₃ reacts with two OH⁻to form carbonate (CO₃ ⁼), therebysuppressing the reaction of OH⁻with TFE to form difluoroacetic acid.Therefore, one mole of CO₂ will neutralize OH⁻from the reaction of twomoles of TFE, or other fluoroolefin with SO₃ ⁼. If TFE if supplied inthe form of TFE:CO₂ shipping mixture, typically about 30/70 mole ratio,it may be used directly, recognizing that CO₂ is in excess of thestoichiometric amount for OH⁻neutralization. Preferably, the shippingmixture is treated before use, such as by membrane separation, to bringthe mole ratio closer to the stoichiometric 66:33 (TFE/CO₂), such as inthe range about 50:50 to about 75:25, more preferably about 60:40 to70:30, and most preferably about 64:36 to 68:32.

Alternatively, fluoroolefin and CO₂ may be added in separate streams inthe desired ratio, or the CO₂ addition may be controlled by means thatmonitor the reaction solution pH and adjust CO₂ addition rate tomaintain pH in the desired range.

It is preferred that, for reagents that are ionic, those with alkalimetal cations be used, preferably the sodium or potassium ion, morepreferably the potassium ion. These cations are also referred to hereinas counter ions to the hydrofluoroalkanesulfonates.

Contrary to the teaching of the prior art, it is not desirable, letalone beneficial, to have radical initiators, particularly radicalinitiators capable of initiating the polymerization of fluoroolefins,present in the reaction mixture and preferably no free radical initiatoris added. Furthermore, oxygen should preferably be excluded from thereaction vessel, since oxygen is capable of initiating polymerization offluoroolefins, especially of TFE. When the fluoroolefin to be used inthe reaction is TFE, it is particularly important to exclude oxygen orinitiators because TFE polymerization proceeds vigorously withsubstantial generation of heat. For less easily polymerizablefluoroolefins, such as HFP, safety considerations related to oxygen areless critical. However, fluoroolefins are costly and initiators andoxygen cause side reactions that compete with formation ofhydrofluoroalkanesulfonic acid, reducing yield and creating uselessbyproducts that can foul the reactor and cause plugging in lines. Inaddition, oxygen reacts with sulfite to form sulfate. Since the sulfiteconcentration is important to controlling the pH of the reaction, suchoxidation by oxygen is undesirable.

In the process according to this invention, a suitable vessel,preferably of stainless steel or other corrosion resistant metal, ischarged with aqueous sulfite solution. The solution may be preparedoutside the vessel, or made in situ, by charging water and dryingredients. It is preferred that the water be deionized andoxygen-free. If it is desired to avoid handling dry ingredients, thesulfite solution may be prepared by adding sulfur dioxide (SO₂) toaqueous caustic, preferably sodium or potassium hydroxide. pH of thesolution should be adjusted to about 4-12. If a sulfite salt, such assodium or potassium sulfite is the sulfite source, sulfuric acid is aconvenient acid for pH adjustment.

After the aqueous sulfite is charged, the vessel is cooled to about 0°C. to −40° C., evacuated and then charged with nitrogen or other inertgas at least once and preferably 2 to 3 times to eliminate oxygen,particularly if TFE is to be the fluoroolefin. The vessel is evacuatedand then charged with the fluoroolefin, closed, and heating is begun.Temperature is raised to about 125° C. and held there with stirring,shaking, or other means of agitating the vessel contents for about 2 to12 hours. If the fluoroolefin is a gas, progress of the reaction may bemonitored by the drop in pressure as the fluoroolefin is consumed. Atthe end of the reaction time, the vessel is cooled to room temperature,vented, and the contents discharged.

The aqueous contents are concentrated by removal of water, preferably atreduced pressure, preferably in a rotary evaporator. More preferably,water-removal in the rotary evaporator is not carried to the point ofdryness. Rather, water is further removed by freeze drying. Freezedrying results in a finely divided, easily handled, low moisture solidthat on treatment with oleum gives yields superior to those obtainedfrom non-freeze dried solids, which tend to be hard and lumpy. Theproduct from the freeze drier preferably contains less than about 5 wt %water, more preferably contains less than about 1 wt % water, and mostpreferably contains less than about 0.5 wt % water.

Also preferable, is the removal of water by spray-drying the aqueousreaction product.

If the potassium salt of the sulfite reactant is used in reaction withHFP or higher fluoroolefins, it is surprisingly found that, upon coolingafter the reaction is ended, the product precipitates in good yield andhigh purity without further treatment, apart from drying. Thus, inaccordance with a preferred form of the invention, conditions areemployed which cause the potassium salt to precipitate from solution.Preferably, cooling is to less than about 15° C., more preferably toless than about 10° C., and most preferably to less than about 5° C.Cooling preferably should not be so low as to cause freezing of thereactor contents.

The discovery of the easy recovery in high purity and high yield of thepotassium salt of the sulfonate product of the reaction of sulfite withHFP or higher molecular weight fluoroolefin, make the potassium salt apreferred salt in the process according to this patent. In addition, ifthe sulfonate salt is isolated without conversion to the sulfonic acid,it is a convenient source of anion in the production of ionic liquidsand photoacid generators.

The preferred potassium salts of products according to this high purity,high conversion synthesis are those of the general formulaR_(f)−CFH−CF₂SO₃K, wherein R_(f) is selected from the group consistingof fluoroalkyl groups, perfluoroalkyl groups, cyclofluoroalkyl groups,and cycloperfluoroalkyl groups, said groups optionally containing etheroxygen.

When the desired final product is the acid, after water-removal, theproduct is directly treated with oleum. The term “oleum” means sulfuricacid (H₂SO₄) containing sulfur trioxide (SO₃), preferably in the rangeof about 1 to 15 wt %. The oleum is preferably used in a weight ratio ofat least about 1 part oleum per part dried product. By using oleum,rather than concentrated sulfuric acid, which generally contains from2-5 wt % water, formation of hydrofluoroalkanesulfonic acid hydrate isavoided. The acid hydrates, for example of TFESA or of the acid derivedfrom HFP, are waxy solids at room temperature. They can solidify in thecondenser during distillation unless the temperature of the condensercoolant is controlled, which is a burdensome requirement.

Commercially available oleum may have too high an SO₃ content. If so,the SO₃ concentration can be reduced by mixing the commercial oleum withsulfuric acid. The sulfuric acid addition dilutes the commercial oleum,and water in the sulfuric acid reacts with some of the SO₃ to formsulfuric acid. The result is oleum of lower SO₃ concentration.

Addition of the oleum gives a slurry, which, on heating in the still,may form a solution, depending on the particular sulfonic acid.

A large excess of oleum is not desirable. It can lead to reduced yieldsof the sulfonic acid and formation of lower boiling product, believed tobe sulfonic acid ester. In the process there should be a small amount,preferably no more than about 5 wt %, more preferably no more than about3 wt %, most preferably no more than about 1 wt %, of low boilingmaterial coming off the distillation before the desired sulfonic acidproduct. This ensures that no hydrate remains to foul the still. Lowboiling material in excess of this is an indication that too much oleumis being used, and the amount should be reduced.

The term “directly treating” with oleum means that no interveningextraction steps are used and the oleum is mixed or contacted with theproduct for treatment. The oleum mixture is then heated to boiling andthe product acid distilled off. If the acid is found to be in hydrateform, that is combined with water, stronger oleum or more complete waterremoval from the product is desirable to avoid additional process steps,such as treatment of the acid hydrate with thionyl chloride to make theunhydrated acid.

The process as described above may be carried out as a batch process.The process according to this invention may also be run continuously,with continuous or periodic drawing off of the liquid contents of thereactor and continuous or periodic replenishment of reactants.

EXAMPLE 1

Example 1, parts A-F, illustrate the steps of a process of the inventionwith TFE as the fluoroolefin prior to the step of directly treating witholeum to produce the hydrofluoroalkane sulfonic acid. Carrying out thereaction with sulfite at a pH of about 4 to about 12, suppresses theundesirable hydration reaction of the fluoroolefin with its attendantproduction of a carboxylic acid byproduct, in the case of TFE,difluoroacetic acid. Parts A-C employ a sodium sulfite solution and thepH is adjusted with sulfuric acid. Parts D-F show the effectiveness ofCO₂, in the absence of any adjustment of pH by acid addition, inpreventing significant production of difluoroacetic acid.

Part A

A Hastelloy® C276 vessel (shaker tube) is used. A solution is preparedof sodium sulfite (23.94 g) and deionized water (90 ml) and the pHadjusted to 5.59 with sulfuric acid to give a solution of final volume130 ml. The solution is loaded into the tube and the tube cooled,evacuated and purged with nitrogen. Following this, tetrafluoroethylene(TFE, 38 g) is loaded to the tube. The starting temperature of the tubeis −32.3° C., and the temperature is raised to 125° C. over 2.5 hours.The pressure, during this temperature rise, increases from 182 psig(1360 kPa) to 545 psig (3860 kPa). The temperature of 125° C. ismaintained for 12 hours, during which time the pressure drops quickly(within 2 hours) from 545 psig (3760 kPa) to 353 psig (2530 kPa) andthen remains approximately constant. The reaction is allowed to cool toroom temperature before venting excess gases and rinsing the reactionmixture from the shaker tube with deionized water. The final pH of thereaction mixture is 7.25.

The water is removed from the reaction mixture under reduced pressure ina rotary evaporator to give 51 g of product. A sample of the resultingsolid analyzed by ¹H NMR in D₂O to contain <1% difluoroacetic acid.Fluorine (¹⁹F) NMR (D₂O) δ−122.0 dt, ³J_(FH)=6 Hz, ³J_(FF)=6 Hz, 2F);−136 (dt, ²J_(FH)=53 Hz, 2F), consistent with tetrafluoroethanesulfonate(TFES-Na).

Proton (¹H) NMR (D₂O) δ 6.4 (tt, ²J_(FH)=53 Hz, ³J_(FH)=6 Hz, 1H). Aportion of the crude sodium tetrafluoroethanesulfonate (TFES-Na) isextracted with four times its weight of acetone, filtered, and theacetone removed in a rotary evaporator. The product contains >99% of(TFES-Na) as shown by NMR and chemical analysis.

Part B

In the same vessel as in Example 1, a solution is prepared of sodiumsulfite (23.94 g) and deionized water (90 ml) and the pH adjusted to5.67 with sulfuric acid to give a solution of final volume 130 ml. Thesolution is loaded into the shaker tube (detailed above) and the tubecooled, evacuated and purged with nitrogen. Following this, TFE (38 g)is loaded to the tube. The starting temperature of the tube is −22.1°C., and the temperature is raised to 125° C. over 75 minutes. Thepressure, during this temperature rise, increases from 205 psig (1515kPa) to 594 psig (4200 kPa). The temperature of 125° C. is maintainedfor 3.5 hours, during which time the pressure drops quickly from 594psig (4200 kPa) to 372 psig (2660 kPa) and then remains constant. Thereaction is allowed to cool to room temperature before venting excessgases and rinsing the reaction mixture from the shaker tube withdeionized water. The final pH of the reaction mixture is 7.25.

The water is removed from the reaction mixture under reduced pressure ina rotary evaporator to give 49 g of product. A sample of the resultingsolid analyzed by ¹H NMR in D₂O to contain <0.1% difluoroacetic acid.¹⁹F NMR (D₂O) δ−122 dt, ³J_(FH)=6 Hz, ³J_(FF)=6 Hz, 2F); −136.2 (dt,²J_(FH)=53 Hz, 2F), consistent with tetrafluoroethanesulfonate(TFES-Na).

¹H NMR (D₂O) δ 6.4 (tt, ²J_(FH)=53 Hz, ³J_(FH)=6 Hz, 1 H).

A portion of the crude sodium tetrafluoroethanesulfonate (TFES-Na) isextracted with four times its weight of acetone, filtered, and theacetone removed in a rotary evaporator. The product contains >99% of(TFES-Na) as shown by NMR and chemical analysis.

Part C

In the same vessel as in Example 1, a solution is prepared of sodiumsulfite (12.6 g) and deionized water (100 ml) and the pH adjusted from10.06 to 5.53 with concentrated sulfuric acid. The solution is loadedinto the shaker tube (detailed above) and the tube cooled, evacuated andpurged with nitrogen. Following this, TFE (10 g) and carbon dioxide(13.2 g) are loaded to the tube. The starting temperature of the tube is−28.8° C., and the temperature is raised to 125° C. over 75 minutes. Thepressure, during this temperature rise, increases from 109 psig (855kPa) to 369 psig (2650 kPa). The temperature of 125° C. is maintainedfor 12.5 hours, during which time the pressure drops steadily from 369psig (2550 kPa) to 272 psig (1875 kPa). The reaction is allowed to coolto room temperature before venting excess gases and rinsing the reactionmixture from the shaker tube with deionized water. The final pH of thereaction mixture is 6.19.

The water is removed from the reaction mixture under reduced pressure ina rotary evaporator to give 20.3 g of product. A sample of the resultingsolid analyzed by ¹H NMR in D₂O to contain <0.1% difluoroacetic acid.¹⁹F NMR (D₂O) δ−121.9 dt, ³J_(FH)=6 Hz, ³J_(FF)=6 Hz, 2F); −136.2 (dt,²J_(FH)=53 Hz, 2F), consistent with tetrafluoroethanesulfonate(TFES-Na).

¹H NMR (D₂O) δ 6.4 (tt, ²J_(FH)=53 Hz, ³J_(FH)=6 Hz, 1 H).

A portion of the crude sodium tetrafluoroethanesulfonate (TFES-Na) isextracted with four times its weight of acetone, filtered, and theacetone removed in a rotary evaporator. The product contains >99% of(TFES-Na) shown by NMR and chemical analysis.

This Example shows that the reaction proceeds well in the presence ofCO₂.

Part D

Using the same vessel as in Example 1, sodium sulfite (6.3 g) and water(100g) are loaded into the shaker tube (detailed above) and the tubecooled, evacuated and purged with nitrogen. Following this, TFE (10 g)and carbon dioxide (22 g) are loaded to the tube. The startingtemperature of the tube is −19.4° C., and the temperature is raised to125° C. over 75 minutes. The pressure, during this temperature rise,increases from 277 psig (1210 kPa) to 833 psig (5850 kPa). Thetemperature of 125° C. is maintained for 5 hours, during which time thepressure drops steadily from 833 psig (5850 kPa) to 770 psig (5410 kPa).Following a power outage, the temperature is raised back to 125° C. from110° C. and maintained for four hours, during which time the pressure isconstant. The reaction is allowed to cool to room temperature beforeventing excess gases and rinsing the reaction mixture from the shakertube with deionized water. The final pH of the reaction mixture is about8. The water is removed from the mixture under reduced pressure and asample of the resulting solid analyzed by proton NMR in D₂O to contain<0.1% difluoroacetic acid.

Part E

Using the same vessel as in Example 1, sodium sulfite (12.6 g) and water(100 g) are loaded into the shaker tube (detailed above) and the tubecooled, evacuated and purged with nitrogen. Following this, apre-combined mixture of TFE (10 g) and carbon dioxide (13 g) (23 gtotal) are loaded to the tube. The starting temperature of the tube is−20° C., and the temperature is raised to 125° C. over 60 minutes. Thepressure, during this temperature rise, increases from 274 psig (1990kPa) to 598 psig (4125 kPa). The temperature of 125° C. is maintainedfor 12 hours, during which time the pressure drops steadily from 598psig (4225 kPa) to 554 psig (3920 kPa). The reaction is allowed to coolto room temperature before venting excess gases and rinsing the reactionmixture from the shaker tube with deionized water. The final pH of thereaction mixture is between 7 and 8. A sample of the solution is dilutedin D₂O and analyzed by 1 H NMR to contain <0.1% difluoroacetic acid.

Part F

A 1-liter Hastelloy C276 stirred reaction vessel is charged with asolution of 53 g anhydrous sodium sulfite (Na₂SO₃, 98%, Acros, 0.42 mol)and 300 ml of deionized water. The pH of this solution is 10.3. Thevessel is held at 25° C., evacuated to atmospheric pressure, and purgedwith nitrogen. The evacuate/purge cycle is repeated four more times. Tothe vessel is then added 450 psig (3.2 MPa) of a 26/74 mol % mixture oftetrafluoroethylene and carbon dioxide (approximately 36 g TFE). Thevessel is heated to 125° C. with agitator speed of 1000 rpm at whichtime the inside pressure is 650 psig (4.60 MPa). The reaction is allowedto proceed at this temperature for 4 hr during which time the pressuredrops to 440 psig (3.14 MPa). The vessel is vented and cooled to 25° C.The pH of the colorless reaction solution is 8.0 which shows thatdissolved carbon dioxide in the form of carbonic acid is indeedfunctioning as a buffer.

The water is removed in vacuo on a rotary evaporator to produce a wetsolid. The solid is then placed in a vacuum oven (120° C., 80 Torr) for4 hr to reduce the water content to approximately 0.9 wt. % (82 g crudematerial). The crude TFES-Na is purified and isolated by extraction with800 ml reagent grade acetone, filtration, and drying to give 57 g ofproduct.

19F NMR (D₂O) δ−121.8 dt, ³J_(FH)=6 HZ, ³J_(FF)=6 Hz, 2F); −135.9 (dt,²J_(FH)=53 Hz, 2F).

1 H NMR (D₂O) δ66.4 (tt, ²J_(FH)=53 Hz, ³J_(FH)=6 Hz, 1 H). % Water byKarl-Fisher titration: 0.9 wt. %.Melting point (DSC) 298° C.TGA (air): 10% wt. loss at 382° C., 50% wt. loss at 424° C.TGA (nitrogen): 10% wt. loss at 377° C., 50% wt. loss at 431° C.

EXAMPLE 2

Example 2 illustrates the reaction of TFE in a process of the invention.A 1-gallon Hastelloy® C276 reaction vessel is charged with a solution of176 g potassium bisulfite hydrate (KHSO₃·H2O, 95%, Aldrich, 1.0 mol),610 g potassium metabisulfite (K₂S₂O₅, 99%, Mallinckrodt, 2.8 mol) and2000 ml of deionized water. The pH of this solution is 5.8. The vesselis cooled to 18° C., evacuated to −3 psig (80 kPa), and purged withnitrogen. The evacuate/purge cycle is repeated two more times. To thevessel is then added 66 g tetrafluoroethylene (TFE) and it is heated to100° C. at which time the inside pressure is 150 psig (1.14 MPa). Thereaction temperature is increased to 125° C. and kept there for 3 hr. Asthe TFE pressure decreases due to the reaction, more TFE is added insmall aliquots (20-30 g each) to maintain operating pressure roughlybetween 150 and 200 psig (1.14 and 1.48 MPa). Once 500 g (5.0 mol) ofTFE has been fed after the initial 66 g precharge, the vessel is ventedand cooled to 25° C. The pH of the clear light yellow reaction solutionis 10-11. This solution is buffered to pH 7 through the addition of 16 gof potassium metabisulfite before workup.

The water is removed in vacuo on a rotary evaporator to produce a wetsolid. The solid is then placed in a freeze dryer (Virtis Freezemobile35xl) for 72 hr to reduce the water content to approximately 1.5 wt %(1387 g crude material). The theoretical mass of total solids is 1351 g.The mass balance is very close to ideal. The isolated solid has slightlyhigher mass due to moisture. This added freeze drying step has theadvantage of producing a free-flowing white powder whereas treatment ina vacuum oven results in a soapy solid cake that is difficult to remove.It has to be chipped and broken out of the flask.

A portion of the crude potassium tetrafluoroethanesulfonate (TFES-K) isfurther purified and isolated by extraction with reagent grade acetone,filtration, and drying. Analysis give the following results:

¹⁹F NMR (D₂O) δ−122.0 dt, ³J_(FH)=6 Hz, ³J_(FF)=6 Hz, 2F); −136.1 (dt,²J_(FH)=53 Hz, 2F). ¹H NMR (D₂O) δ 6.4 (tt, ²J_(FH)=53 Hz, ³J_(FH)=6 Hz,1H).

% Water by Karl-Fisher titration: 580 ppm.Analysis calculated for C₂HO₃F₄SK: C, 10.9: H, 0.5: N, 0.0 Found: C,11.1: H, 0.7: N, 0.2.Melting point by differential scanning calorimeter (DSC) 242° C. Thermalgravimetric analysis (TGA) (air): 10% wt. loss at 367° C., 50% wt. lossat 375° C. TGA (nitrogen): 10% wt. loss at 363° C., 50% wt. loss at 375°C.

A 100 ml round bottom flask with a sidearm is equipped with a digitalthermometer and a magnetic stirbar and placed in an ice bath underpositive nitrogen pressure. To the flask is added 50 g crude TFES-K fromthe previous step along with 30 g of concentrated sulfuric acid (EMScience, 95-98%) and 78 g oleum (Acros, 20 wt % SO₃) while stirring.This amount of oleum is chosen so that the SO₃ reacts with and removesthe water in the sulfuric acid as well as in the crude TFES-K whilestill being present in slight excess. The mixing causes a small exothermwhich is controlled by the ice bath. Once the exotherm is over, adistillation head with a water condenser is placed on the flask and itis heated under nitrogen behind a safety shield. The pressure is slowlyreduced using a PTFE membrane vacuum pump (Buchi V-500) in steps of 100Torr (13 kPa) in order to avoid foaming. A dry-ice trap is also placedbetween the distillation apparatus and the pump to collect any excessSO₃. Once the pot temperature reaches 120° C. and the pressure is heldat 20-30 Torr (2.7-4.0 kPa) a colorless liquid starts to reflux andlater distills at 110° C. and 31 Torr (4.1 kPa). A forerun oflower-boiling impurity (2.0 g) is obtained before collecting 28 g of thedesired colorless acid, TFESA.

In the 50 g of impure TFES-K, it is calculated that approx. 39.8 gTFES-K is present. Thus, the 28 g of product is an 85% yield of TFESAfrom TFES-K as well as an 85% overall yield from TFE. Analysis gives thefollowing results: ¹⁹F NMR (CD₃OD) δ−125.2 dt, ³J_(FH)=6 Hz, ³J_(FF)=8Hz, 2F); −137.6 (dt, ²J_(FH)=53 Hz, 2F). ¹H NMR (CD₃OD) δ 6.3 (tt,³J_(FH)=6 Hz, ²J_(FH)=53 Hz, 1H).

EXAMPLE 3

This example demonstrates the reaction of hexafluoropropylene (HFP)according to this invention. A 1-gallon Hastelloy® C276 reaction vesselis charged with a solution of 25 g anhydrous sodium sulfite (Na₂SO₃,98%, Acros, 0.20 mol), 73 g sodium bisulfite (NaHSO₃, Aldrich, 0.70 mol)and 400 ml of deionized water. The pH of this solution is 5.7. Thevessel is cooled to 4° C., evacuated to −3 psig (80.6 kPa), and thencharged with 120 g of hexafluoropropylene (HFP, 0.8 mol, 48 psig (430kPa)). The vessel is heated with agitation to 120° C. and kept there for3 hr. The pressure rises to a maximum of 250 psig (1825 kPa) and thendrops down to 25 psig (275 kPa) within 30 minutes. At the end, thevessel is cooled and the remaining HFP is vented and the reactor ispurged with nitrogen. The final solution has a pH of 7.3.

The water is removed in vacuo on a rotary evaporator to produce a wetsolid. The solid is then placed in a vacuum oven (150 Torr (20 kPa),140° C., 48 hr) to produce 219 g of white solid which containedapproximately 1 wt % water. The theoretical mass of total solids is 217g.

A 100 ml round bottom flask with a sidearm is equipped with a digitalthermometer and a magnetic stirbar and placed in an ice bath underpositive nitrogen pressure. To the flask is added 50 g crude sodiumhexafluoropropanesulfonate (HFPS-Na) from the previous step along with30 g of concentrated sulfuric acid (EM Science, 95-98%) and 58.5 g oleum(Acros, 20 wt % SO₃) while stirring.

This amount of oleum is chosen so that the SO₃ will react with andremove the water in the sulfuric acid as well as in the crude HFPS-Nawhile still being present in slight excess. The mixing causes a smallexotherm which is controlled by the ice bath. Once the exotherm is over,a distillation head with a water condenser is placed on the flask, whichis heated under nitrogen behind a safety shield. The pressure is slowlyreduced using a PTFE membrane vacuum pump (Buchi V-500) in steps of 100Torr (13 kPa) to avoid foaming. A dry-ice trap is also placed betweenthe distillation apparatus and the pump to collect any excess SO₃. Whenthe pot temperature reaches 100° C. and the pressure is held at 20-30Torr (2.7-4 kPa) a colorless liquid started to reflux and laterdistilled at 118° C. and 23 Torr (3.1 kPa). A forerun of lower-boilingimpurity (1.5 g) is obtained before collecting 36.0 g of the desiredacid, hexafluoropropanesulfonic acid (HFPS).

In the 50 g of impure HFPS-Na, it is calculated that approx. 44 gHFPS-Na is present. Thus, the 36.0 g of HFPS product is an 89% yieldfrom HFPS-Na as well as an 84% overall yield from HFP.

The crude HFPS-Na from the vacuum oven drying step is further purifiedand isolated by extraction with reagent grade acetone, filtration, anddrying.

¹⁹F NMR (D₂O) δ−74.5 m, 3F); −113.1, −120.4 (ABq, J=264 Hz, 2F); −211.6(dm, 1F). ¹H NMR (D₂O) δ5.8 (dm, ²J_(FH)=43 Hz, 1H).

Melting point (DSC) 126° C.TGA (air): 10% wt. Loss at 326° C., 50% weight loss at 446° C.TGA (N₂): 10% wt. loss at 322° C., 50% weight loss at 449° C.

EXAMPLE 4 Synthesis of Potassium 1,1,2,3,3,3-Hexafluoropropanesulfonate(HFPS-K)

This example demonstrates the surprising superiority of the synthesisusing the potassium salt of the sulfite reactants to make the potassiumsalt of 1,1,2,3,3,3-hexafluoropropanesulfonate in high purity and goodyield without special separation and purification steps.

A 1-gallon Hastelloy C276 reaction vessel is charged with a solution of130 g (0.74 mol) potassium sulfite hydrate (K2SO3·xH2O, 95%, Aldrich),448 g (2.02 mol) potassium metabisulfite (K2S2O5, 99%, Mallinckrodt) and1300 mL of deionized water. The pH of this solution is 6.1. The vesselis cooled to −35° C., evacuated to −3 psig (83 kPa), and purged withnitrogen. The evacuate/purge cycle is repeated two more times. To thevessel is then added 550 g (3.67 mol) hexafluoropropylene (HFP) and itis heated to 125° C. During heating, the internal pressure increased toa maximum of 320 psig (2.3 MPa) at 80° C., then rapidly dropped to 23psig (260 kPa) within the next 20 min. The total reaction time from thestart of heating is 75 min. The vessel is then vented and cooled to 25°C.

The reaction product is a white precipitate in a mother liquor of pH7.0. The crude reaction mixture is cooled to 5° C. and vacuum filteredto isolate the solid product which is further dried in vacuo (70° C., 40Torr (5 kPa), 48 hr) to afford 788 g (2.92 mol) of white powderedproduct (80% yield).

Water by Karl-Fisher titration: 0.15 wt %.

Analysis Calculated for C3HO4SF6: C, 13.3: H, 0.4: N, 0.0.

Found: C, 13.5; H, 0.4: N, 0.1.

It is seen that the product precipitates in 80% yield and high purity oncooling of the reaction mixture. This is unlike the behavior of thesodium salt in Example 3, where the cooled reaction mixture is asolution without significant precipitate, and in which evaporation isnecessary to recover the salt, which then requires further purification.

EXAMPLE 5 Synthesis of Potassium 1,1,2,3,3,3-Hexafluoropropanesulfonate(HFPS-K)

Example 4 is repeated except that the amount of water is reduced to 1000ml. The product precipitates in 85% yield and the same high purity foundin Example 4.

1. The potassium salts of R_(f)-CFH-CF₂SO₃ ⁻, wherein R_(f) is selectedfrom the group consisting of fluoroalkyl groups, perfluoroalkyl groups,cyclofluoroalkyl groups and cycloperfluoroalkyl groups, said groupsoptionally containing ether oxygen.
 2. Potassium1,1,2,3,3,3-hexafluoropropanesulfonate.